Chemical screens provide a valuable approach for identifying small molecules that can regulate embryogenesis and control biological processes. With the identification of chemical compounds from specific assays, it is possible to define the temporal inductive events that establish embryonic differentiation pathways. Furthermore, an advantage of chemical screens over genetic screens includes the identification of molecules that may possess the ability to function in multiple organisms. Whole organism chemical screens also allow for rapid validation of chemical compounds by eliminating toxic and non-specific compounds often found in high-throughput screening. The Aims outlined in this proposal combine experimental embryology, molecular biology, and high throughput screening technology to identify chemical compounds that influence the earliest molecular events regulating zebrafish development. Model organisms have long served as a tool for drug discovery, but whole organism screens have not yet found wide application in high-throughput chemical genetics applications. This has been partly because of the relatively greater amounts of compounds required for organisms and the laborious nature of assaying compound effect, which is typically done by visual observation. Nonetheless, because of the growing interest in systems biology and the recognition of the complexities of biological pathways, there is increasing enthusiasm for exploiting organism-based phenotypic assays in an high throughput screening format. In this application, we propose to leverage the strengths and resources of our existing zebrafish and drug discovery programs at the University of Pittsburgh to develop and implement tools and procedures for conducting chemical screens in zebrafish. The drug discovery center has extensive high throughput screening capabilities, including multimode plate readers, an ArrayScanll automated image acquisition and analysis instrument, and automated liquid handlers. The chemical compounds we identify from the assays outlined in this proposal, and the screen technology we adapt to zebrafish research will become important tools for the scientific community.